Oxygen consumption meter

Abstract

An indirect calorimeter for calculating the metabolic rate of a subject by measuring the oxygen consumption during respiration over a period of time includes a gas flow meter providing output electric signals to a microprocessor which drives a display and printer. A carbon dioxide scrubber is connected to the flow meter and a mouthpiece so that inhaled gas passes first through the scrubber and then through the flow meter before being provided to the subject's respiratory system through the mouthpiece. The exhaled gas passes through the scrubber and then through the flow meter. The difference in volume between the inhaled gas and the exhaled gas is proportional to the oxygen consumption of the subject and the microprocessor integrates that signal over the time of the test, and multiplies it by a constant to provide a metabolic rate display. By passing both the inhaled and exhaled gases through the scrubber before their volume is measured, their temperature and humidity are modified to a state of equal temperature and humidity.

Having thus described my invention, I claim: 
     
       1. An indirect calorimeter operative to measure the respiratory oxygen consumption from respiratory gases per unit time of a subject, comprising: a respiratory connector operative to be supported in contact with the subject so as to pass said respiratory gases as the subject breathes into said respiratory connector;   a scrubber having a gas inlet and a gas outlet and constructed to absorb carbon dioxide from said respiratory gases passing between its inlet and outlet;   flow meter means operatively connected to said respiratory connector for generating signals as a function of the gas volume of said gases passed through said meter means;   valves and conduits interconnecting said respiratory connector, scrubber, and flow meter means, and constructed such that upon the subject inhaling, gas is caused to pass through the scrubber, then through the flow meter means, and then to the subject's respiratory system through the respiratory connector, and upon the subject exhaling to pass the exhaled gas from the respiratory connector first through scrubber, then through the flow meter means;   means for receiving the resultant signals from the flow meter means and for generating a signal proportional to the integral of the differences between the inhaled and exhaled gas volumes over a period of time; and   means for connecting said conduits to a mechanical ventilator so that the ventilator may provide respiratory gas to the calorimeter and receive exhaled gas from the calorimeter.   
     
     
       2. The indirect calorimeter of claim 1 wherein the mechanical ventilator includes a single passage adapted to pass both inflow to the ventilator and outflow from the ventilator and said means for connecting said conduits to said mechanical ventilator includes a single conduit interconnecting said single passage to said respiratory connector, scrubber, and flow meter means, and constructed to pass respiratory gasses through said single passage of the ventilator. 
     
     
       3. The indirect calorimeter of claim 1 wherein said ventilator includes a first tube for passing gasses to be inhaled by the subject and a second tube to pass gasses exhaled by the subject, and said first and second tubes constructed to connect to separate sections of said conduits of the indirect calorimeter interconnecting said respiratory connector, scrubber and flow meter means. 
     
     
       4. The indirect calorimeter of claim 3 including a first one-way valve means for interconnecting said first tube of the ventilator with the conduits of the indirect calorimeter and a second one-way valve means for interconnecting the second tube of the ventilator to the indirect calorimeter. 
     
     
       5. The indirect calorimeter of claim 1 wherein said conduits have disposed therein a first pair of valves operably connected to said inlet side of the scrubber and adapted to connect the scrubber to a respiratory connector and a second pair of valves operably connected to said outlet side of the scrubber and adapted to connect the scrubber to a source and sump of respiratory oxygen.